Key et al, U.S. Pat. No. 6,701,861 discloses a semi-submersible floating production vessel which has a ring pontoon with three main columns extending upwardly from corners of the pontoon and three secondary, minor columns extending upwardly from centers of the triangular sides. The columns support an open frame deck, on which production modules are positioned. The vessel is adapted for semi-permanent mooring with pre-tensioned mooring lines that are attached to swivel pad eyes secured on the main columns below the water line. Production and export risers are connected to the vessel below the water line. A compressed air ballast system allows selective emptying of ballast compartments located in the ring pontoon and eliminates the need for a conventional pump room.
Huang et al, U.S. Pat. No. 6,503,023 discloses a temporary stability module for marine structures and a method for using the modules during the construction, transportation, installation and/or removal of the structure that permit the structure, including platform, deck and equipment to be constructed in an upright position, towed to an ocean installation site, and installed by ballasting the structure or temporary stability modules and subsequent removal of the modules. The removable temporary stability modules are shown attached to an “extended-base” “tension leg” platform having four uniform rectangular support columns disposed about a central axis of the substructure and horizontal pontoons interconnecting adjacent columns at their lower ends. The substructure also includes leg extensions radiating from the columns and/or the pontoons, which are described more fully in U.S. Pat. No. 6,447,208, discussed below.
Huang et al, U.S. Pat. No. 6,447,208 discloses an “extended-base” “tension leg” substructure, and an offshore platform supported on the substructure and a method for supporting an offshore platform on the substructure. The substructure includes a plurality of support columns disposed about a central axis of the substructure and interconnected by at least one pontoon. Each column comprises an above-water portion and a submerged portion. The substructure also includes a plurality of wings or arms radiating from the columns and/or the pontoons, each wing fixedly or removably securing at least one tendon extending from the wing to an anchor on the seabed. The substructure includes an open, wave transparent, central zone for improved access to well-related equipment, conduits or the like and the wings minimize translational movement and rotational flex in the substructure reducing fatigue in the tendons and their connections.
Frimm et al, U.S. Pat. No. 6,015,245 discloses a ring pontoon semi-submersible offshore vessel wherein the vertical centerline of each of the corner columns is located inward of both the axial centerline of the forward section of the ring pontoon and the axial centerline of the aft section of the ring pontoon. Additionally, the vertical centerlines of the corner columns may be located inward with respect to the axial centerlines of the starboard and port portions of the ring pontoon. The superstructure deck may be supported by radial braces extending from the ring pontoon to locations on the superstructure deck, which are inward of the ring pontoon.
Liden, U.S. Pat. No. 4,498,412 discloses a semi-submersible offshore platform having an operating deck carried by four cylindrical uniform columns supported by a pontoon structure comprising four-sided boxes formed into a square ring. Each pontoon box is subdivided into two compartments by a longitudinal centerline bulkhead, the compartments being further subdivided into tanks by transverse bulkheads. Tanks outside the centerline bulkheads are used for ballast water, and tanks inside the centerline bulkheads are used to store the oil produced.
Ludwigson, U.S. published patent application 20010026733, published Oct. 4, 2001, discloses a semi-submersible vessel adapted to resist heave motion that includes a plurality of support columns with a square-shaped ring pontoon connected to their lower ends. The axial centerline of the square-shaped ring pontoon intersects the axial centerline of the lower ends of the support columns, and the support columns are inclined upwardly and inwardly from the ring pontoon to the deck.
Wybro et al, U.S. Pat. No. 7,140,317 discloses a central ring pontoon semi-submersible floating platform for use in offshore applications having a hull configuration including vertical support columns, a central pontoon structure disposed inboard of the columns at a lower end thereof, and a deck structure supported at an upper end of the columns. The vertical columns and pontoon structure are constructed substantially of flat plate. The vertical columns are adjoined to the outer periphery of the central pontoon and have a transverse cross sectional shape with a major axis oriented radially outward from a center point of the hull, and a central vertical axis disposed a distance outward from the pontoon outer periphery. Risers can be supported on the inboard or outboard side of the pontoon and extended to the deck, and the structure can be anchored by mooring lines extending along the outboard face of the columns extending radially outward and downward from their lower ends.
Horton, U.S. Pat. No. 6,935,810 discloses a semi-submersible, multicolumn deep draft floating offshore oil and gas oil and production platform comprising a floating hull having an adjustably buoyant base, a plurality of columns vertically upstanding from the base and an equipment deck that is supported atop the columns when the platform is operationally deployed. Each of the columns comprises a cellular structure that includes a plurality of elongated tubes having a variety of cross-sectional shapes extending from the base to the top of the column. Each of the tubes defines one or more closed compartments. At least one of the compartments has buoyancy that is adjustable. The buoyancy of the compartments and the base can be controllably adjusted with pressurized air to provide a safer and less costly method for deploying the platform for offshore operations.
Haselton, U.S. Pat. No. 3,986,471 discloses apparatus for damping vertical movement of a semi-submersible vessel having a small water plan area, whose buoyancy is provided substantially completely by submerged pontoon means and which includes at least one submerged damper plate supported deep beneath the vessel by flexible tensioned support elements, such as chains or cables and which has valves or similar flow controllers therein for providing substantially greater resistance to the upward movement of the plate than the downward movement. The area of the damper plate is several times larger than the water plane area of the vessel and provides low resistance to downward movement and higher resistance to upward movement.
Xu et. al, U.S. Pat. No. 6,652,192 discloses an apparatus for a heave suppressed floating offshore drilling and production platform having vertical columns, lateral trusses connecting adjacent columns, a deep submerged horizontal plate supported from the bottom of the columns by vertical truss legs and a topside deck supported by the columns. During the launch of the platform and towing in relatively shallow water the truss legs are stowed in shafts within each column and the plate is carried just below the lower end of the columns. After the platform has been floated to the deepwater site, the truss legs are lowered from the column shafts to lower the plate to deep draft for reducing the effect of wave forces and to provide heave and vertical motion resistance to the platform.
Wetch, U.S. Pat. No. 6,666,624 discloses a floating platform comprising an uppermost buoyant and ballastable hull partially submerged in water without contacting the floor of the body of water and usually without being moored to the floor of the body of water. The bottom of the uppermost hull is attached to the top of a lower buoyant and ballastable hull after the lower hull has been completely submerged and anchored to the floor of the body of water with flexible mooring.
Srinivasan, U.S. Pat. No. 6,761,124 discloses column stabilized floating structures having a deck and a plurality of vertical buoyant caissons bridged together in distantly spaced relation by plurality of open frame horizontal truss pontoon members and a vertical truss column at the lower end. The buoyancy of the caissons is selectively adjusted by means of ballast control. Water is selectively pumped into and out of the keel tanks at the bottom of the truss structure to raise or lower the center of gravity of the entire mass of the floating structure relative to the center of buoyancy to compensate for different operational, environmental and survival conditions.
Mougin, U.S. Pat. No. 4,241,685 discloses a self-stabilizing offshore floating tower comprising two coaxial cylindrical enclosures interconnected by continuous radial bulkheads forming, in the upper portion, a ring of damping chambers and, in the lower portion, a ring of buoyancy tanks around a bell-shaped chamber which is partially filled with air to produce pneumatic damping of vertical movement of the tower. The upper portion of the tower is separated from the lower portion by a horizontal slab, and the upper portion of the internal enclosure is perforated in the vicinity of the horizontal slab.
Horton U.S. Pat. No. 6,817,309 discloses a floating hull for a single-column spar-type offshore oil and gas drilling and production platform which comprises a plurality of parallel tubular cells that are subdivided into compartments having a buoyancy controlled by one or both of fixed and variable ballast. The cells include side wall openings for admitting and discharging seawater and petroleum ballast with pumps. Fixed and/or variable ballast may be disposed on or in the cells to adjust buoyancy, trim, and stability. Lower and upper portions of the cells may extend above or below the others for trim or stability. Longitudinal recesses may be formed in an exterior peripheral surface for routing of mooring lines and piping. Stepped helical strakes can be disposed on an outer peripheral surface of the platform or some of the cells to reduce vortex-induced vibrations of the platform.